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The epidemiological tool-box. A ssociations – quantification using rate ratios, rate differences, odds ratios. Analytical epidemiology 1: Ecological Studies. The association between quantity of salt sold and oesophageal cancer mortality in counties of Henan province, China.

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the epidemiological tool box
The epidemiological tool-box
  • Associations – quantification using rate ratios, rate differences, odds ratios
slide2

Analytical epidemiology 1: Ecological Studies

The association between quantity of salt sold and oesophageal cancer mortality in counties of Henan province, China
slide5
Risk for cancer of the liver (cases/100000 population in areas of high risk for this cancer - sub Saharan Africa and eastern Asia
the epidemiological tool box1
The epidemiological tool-box
  • Biases– information bias, selection bias
  • Confounding – detection and control
  • Determination of causation
  • Effect Modification/ Interaction/Synergism
design of a case control study
Design of a case-control study

TIME

direction of inquiry

Exposed

Cases with disease

Unexposed

Population

Controls without disease

Exposed

Unexposed

design of a cohort study
Design of a cohort study

TIME

direction of inquiry

people exposed disease

population without the no disease

disease

not exposed disease

no disease

“at risk”

analytical studies 3 cohort of british doctors
Analytical studies 3:Cohort of British Doctors

Death by lung cancerCurrent smokerNon smoker

Yes a (4,180) b (224)

No c (45,820) d (39,776)

# at beginning 50,000 40,000

Total 90,000

cohort of british doctors cont d
Cohort of British Doctors cont’d

Relative risk: risk in exposed/risk in unexposed

RR = a  b = 0.084 .0056 = 14.9

a+c b+d

Attributable risk = risk difference = excess risk in smokers

= 0.084 - 0.0056 = .078

slide13
Analytical studies 3: Shanghai - cohort study 18,000 men-synergy(Qian G-S et al, Can Epid Biom. Prev 1194;33)

Note: Aflatoxins measured by adducts, interview unreliable

slide14

Effect Modification (or Interaction) is said to occur when the association between exposurex and outcomey differs by variablez

prevalence of actinic keratosis in israeli dermatologic patients with and without psoriasis
Prevalence of Actinic keratosis in Israeli Dermatologic Patients with and without Psoriasis

51 (11%)

200 (27%)

538 (73%)

409 (89%)

Psoriatics

Controls

what is actinic keratosis
What is actinic keratosis?
  • Rough scaly spots on sun-damaged skin
  • Pre-cancerous (can give rise to Squamous cell caricnoma SCC)
  • Found on nose, cheeks, upper lips, temples, forehead
  • Common in fair-skinned people and those in outdoor occupations
adjusted odds ratios or for solar keratosis by hair color comparing psoriatics and controls
Adjusted odds ratios (OR) for solar keratosis by hair color comparing psoriatics and controls

Adjusted for ethnic origin, gender, age and degree of sun exposure

slide18
Adjusted odds ratios (OR) for solar keratosis by propensity to sunburn comparing psoriatics and controls

Sometimes

Adjusted for ethnic origin, gender, age and degree of sun exposure

the epidemiological tool box2
The epidemiological tool-box
  • Formulating study question
  • Gathering data
  • Hypothesistesting
  • Impact measures
the epidemiological tool box3
The epidemiological tool-box
  • Judging the methodology
  • Kappa statistic & Reliability
  • Life Expectancy – survival analysis, life table analyses
the epidemiological tool box4
The epidemiological tool-box
  • Measurement accuracy
  • N = sample size
  • Outcome Measures
  • Proportional mortality/morbidity
the epidemiological tool box5
The epidemiological tool-box
  • Quality of data (and/or life!)
  • Randomization; Risk – incidence, types of incidence, incidence vs. prevalence, crude vs. disease-specific
the epidemiological tool box6
The epidemiological tool-box
  • Standardization
  • Time Trends
  • Utility assessment
  • Validity
  • Weight of evidence
the epidemiological tool box7
The epidemiological tool-box
  • X-axis
  • Y-axis and plotting the data
  • Z-score and statistical inference
  • Ж - ?????
slide25

You have made an observation based on descriptive cancer statistics…….

Steps in Designing and Conducting an

Epidemiologic Investigation

slide26

Specify TOPIC and PURPOSE

  • Determining what is KNOWN and UNKNOWN
  • State the CASE FOR ACTION
slide27

Formulate STUDY OBJECTIVES

  • Formulate HYPOTHESES

“There are two possible outcomes: If the result confirms the hypothesis, then you've made a measurement. If the result is contrary to the hypothesis, then you've made a discovery”

- Enrico Fermi, Physicist, 1901-1954

slide28

Select appropriate STUDY DESIGN

  • Choose & define STUDY VARIABLES
  • Define STUDY POPULATION & SELECTION TECHNIQUES
  • Develop DATA COLLECTION TOOLS
slide29

PRETEST developed instruments

  • TRAIN FIELD WORKERS
  • CONDUCT/MONITOR FIELD WORK
  • Prepare data for ANALYSIS
  • ANALYSE the data
slide30

WRITE-UP findings

  • COMMUNICATE findings
  • INCORPORATE results into health planning
  • EVALUATE modified health program
slide31

It is easier to investigate problems than to solve them.

BUT…

It’s not so easy to study them either!